In the electronic industry electronic circuits have become more and more compact to the point that small portable circuit cards have been developed that can be removably inserted into electronic equipment typically for temporary use. In particular, external memory circuit cards have been developed which approximate the size of credit cards, though somewhat thicker, and which incorporate a circuit board sandwiched between metal or plastic covers, and an electrical connector for connection to external electronic equipment.
Cartridges enclosing storage devices for programs such as games have been in use for many years particularly for video games and some microcomputers. Because of their relatively large size physical durability was not a property that was difficult to develop for cartridges. Space was available to build the necessary strength into the components and housings. However, for a circuit card package the size of a credit card physical construction techniques are more limited.
Memory card devices are illustrated in U.S. Pat. No. 4,924,076, issued May 8, 1990 and assigned to Mitsubishi Denki Kabusihiki Kaisha, Japan. The devices illustrated incorporate semiconductor devices mounted in an internal base and enclosed in a plastic package formed from two bonded plastic sections.
Another reference, U.S. Pat. No. 4,798,946, issued Jan. 17, 1989, and assigned to the assignee of the previous mentioned patent describes a plastic package for containing an IC card, which essentially constructs a plastic box from halves glued along mating edges.
It does not appear that the devices referred to in the above references would meet the specifications outlined by the Personal Computer Memory Card International Association (PCMCIA), in September 1991, relating to torque, bend, flex and warpage of credit card sized memory cards. Plastic components do not generally provide sufficient electrical shielding to protect internal electronic components from static electricity, while adhesives used to bond them may fail under stress from heat, humidity and other factors.
Similarly, designs known to the applicant incorporating electronic cards retained by plastic perimeter frames and sandwiched between planar plastic or metal sheets bonded to the frame have not been able to meet the PCMCIA specifications.
U.S. Pat. No. 4,386,388 issued May 31, 1983 and assigned to Northern Telecom Limited describes a printed circuit board assembly which uses a sheet aluminum cover which loosely encloses a circuit board; abutting edges of the cover are held in a contiguous relationship by inturned edges of the cover which engage small notches in end plates on the circuit board. While this assembly may be satisfactory for larger circuit boards, sufficient strength or stiffness is not likely possible for circuit boards approaching the size of credit cards.
Card designs which involve bonding card covers to internal circuit components can produce undesirable stresses on the components and their connections with other components reducing durability.